The present invention relates to the general field of making gas turbine casings out of composite material, and it relates more particularly to gas turbine fan retention casings for aeroengines.
It is common practice for a fan retention casing to be made up firstly of a relatively thin wall defining the air inlet passage into the aeroengine and supporting an abradable material in register with the path followed by the tips of the fan blades, and also supporting an acoustic treatment coating, if any, and secondly of a shield structure that is fastened to said wall on the outside, around the fan, so as to retain debris such as ingested objects or fragments of damaged blades in the event of them being thrown outwards by centrifuging, in order to prevent them from passing through the casing and reaching other portions of the aircraft.
Proposals have already been made for making a fan retention casing out of composite material. By way of example, reference may be made to Document EP 1 961 923, which describes fabricating a casing out of composite material of varying thickness, by forming fiber reinforcement out of superposed layers of a fiber texture and densifying the fiber reinforcement with a matrix. More precisely, that document makes provision for using a take-up mandrel for three-dimensional weaving of the fiber texture, which texture is then wound as superposed layers onto an impregnation mandrel having a profile corresponding to the profile of the casing that is to, be made. The fiber preform as obtained in that way is held on the impregnation mandrel and is impregnated with resin prior to polymerizing the resin.
In practice, performing that method raises the problem of transferring the fiber texture from the take-up mandrel to the impregnation mandrel and of controlling the position of the fiber texture during winding. Indeed, any drift of the position of the fiber texture during winding would result in localized departures from tolerance concerning tension, offset, and fiber density and that would then make the fiber texture unusable.
Moreover, the casing is made by winding several turns around the preform (typically four), which means that, after winding, it is not possible to inspect the positions of warp tracers (used for monitoring alignment) for those successive turns. It is thus imperative to ensure correct positioning of the fiber texture during winding, and also to have an inspection report after winding, making it possible to certify that the fiber texture complies with specifications, which means that it is also necessary to ensure full control over offset of the fiber texture in real time.
Consequently, there exists a need to have a winding machine that makes it possible, during the transfer of the fiber texture from the take-up mandrel to the impregnation mandrel, to ensure both that the fiber texture is correctly placed and applied on the impregnation mandrel and that the alignment of the fiber texture is controlled in real time and possibly offset. Indeed, after winding, it is impossible to verify the position and the offset of the fiber texture and it is thus impossible to validate the winding operation.